The good insulation performance of sulfur hexafluoride (SF6) gas makes a gas insulating switch gear compact and contributes to reduction in the space of an electric chamber. In a vacuum circuit breaker installed in this gas insulating switch gear, the operation mechanism of the vacuum circuit breaker is generally disposed outside the gas container, the main circuit portion of the vacuum circuit breaker is disposed inside the gas container, and the operation mechanism is coupled to the main circuit portion via a drivable shaft while the airtightness between the inside and the outside of the gas container is maintained.
Although the main circuit portion of the vacuum circuit breaker includes an insulation operation rod, a movable side terminal, a vacuum valve, and a fixed side terminal, these structural members of the main circuit portion need to be supported in the gas container while being insulated from the gas container that is kept at the ground potential. Therefore, the main circuit portion of the vacuum circuit breaker is generally supported by an insulator or an insulating holder in the gas container.
When the main circuit portion of the vacuum circuit breaker is supported by the insulating holder as described above, if the insulating holder is formed in, for example, a cylinder to surround the vacuum valve, the electric field outside the vacuum valve becomes high and the withstand voltage performance degrades. In addition, since the vacuum valve is heated during energization, if the vacuum valve is surrounded, the temperature around the vacuum valve rises because the convection of air is suppressed and the energization performance degrades.
A vacuum circuit breaker as indicated in, for example, PTL 1 or PTL 2 has been proposed to solve such problems.
That is, in the vacuum circuit breaker indicated in PTL 1, as illustrated in particularly in FIG. 3, the first insulating frame and the second insulating frame each having a U-shaped cross section are disposed so as to cover the vacuum valve from the left and right sides of the vacuum valve with a clearance left therebetween and the first insulating frame and the second insulating frame are tightened by the fixed side conductor of the vacuum valve.
In addition, as illustrated in FIGS. 1 and 4, the vacuum circuit breaker indicated in PTL 2 includes a pair of insulation support plates disposed so as to sandwich the vacuum valve from the up and down sides and an upper electrode, fixed to one end of the insulation support plate, to which the fixed side of the vacuum valve is fixed.